Transistors are being widely used as switching devices or driving devices in the field of electronic devices. Particularly, thin film transistors (TFTs) may be manufactured on a glass substrate or a plastic substrate, and thus, are being widely used as switching devices for display apparatuses such as liquid crystal display (LCD) devices and organic light emitting devices.
TFTs may be categorized into amorphous silicon TFTs where amorphous silicon is used as an active layer, polycrystalline silicon TFTs where polycrystalline silicon is used as an active layer, and oxide semiconductor TFTs where an oxide semiconductor is used as an active layer, with respect to a material included in an active layer.
In oxide semiconductor TFTs, oxide included in an active layer may form a layer at a relatively low temperature, mobility may be high, a large resistance variation may occur based on a content of oxygen, and desired physical properties may be obtained easily. Also, since an oxide semiconductor is transparent in terms of a characteristic of oxide, the oxide semiconductor TFTs may be easily used to implement transparent display apparatuses.
A high-mobility oxide semiconductor layer has a carrier concentration of 1018/cm3 or more, and thus, when the high-mobility oxide semiconductor layer has a thickness of 10 nm or more, the high-mobility oxide semiconductor layer may have the same characteristic as that of a conductor. In order to prevent the high-mobility oxide semiconductor layer from becoming conductive, the high-mobility oxide semiconductor layer may be manufactured to have a thickness of less than 10 nm and may be applied to TFTs. In this case, however, due to a thin thickness, an oxide semiconductor layer may be damaged or swept away in a patterning process.